When light passes
through a multimode fiber, two-dimensional random
intensity patterns are formed due to complex interference within
the fiber. The extreme sensitivity of speckle patterns to the frequency
of light paved the way for high-resolution multimode fiber spectrometers.
However, this approach requires expensive IR cameras and impedes the
integration of spectrometers on-chip. In this study, we propose a
single-pixel multimode fiber spectrometer by exploiting wavefront
shaping. The input light is structured with the help of a spatial
light modulator, and optimal phase masks, focusing light at the distal
end of the fiber, are stored for each wavelength. Variation of the
intensity in the focused region is recorded by scanning all wavelengths
under fixed optimal masks. Based on the intensity measurements, we
show that an arbitrary input spectrum having two wavelengths 20 pm
apart from each other can be reconstructed successfully (with a reconstruction
error of ∼3%) in the near-infrared regime, corresponding to
a resolving power of R ≈ 105. We
also demonstrate the reconstruction of broadband continuous spectra
with varying bandwidths. With the installation of a single-pixel detector,
our method provides compact detection and a lower budget alternative
to conventional systems, with potential promise to operate at low-signal
levels.
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